Such sensors, especially corrosion sensors, are extremely thin and small (of the order of 2 cm square) and are often placed in inaccessible or difficult to access locations on structures such as drill rigs or vehicles such as aircraft, ships or land vehicles. Corrosion of metallic structures, particularly in corrosive environments such as on seagoing vessels or carrier-based aircraft, is an enormous financial problem for operators and can amount to billions of dollars per annum, as is the case, for example, for the US military. Thus the use of such sensors as corrosion sensors, which can be used to signal various stages of corrosion of a structure on which they are mounted, can give the owner remote information on the state of corrosion of areas which are hard-to-access, are functionally critical or are highly numerous and would otherwise lead to excessive inspection time. Corrosion of the sensor may also be used as an indication of paint degradation or of defects occurring in a layer of paint.
Sensors of this type are both difficult and expensive to manufacture, being fabricated in clean rooms, using silicon chip manufacturing technology.